In order to establish a working connection between a signal transmitter and a signal receiver, on the one hand, and a two-wire line common thereto, on the other hand, use is conventionally made of a so-called hybrid-coil transformer having a split primary winding in series with the line. A transmitting circuit, connected to an intermediate point of the primary winding of this transformer, and a receiving circuit, connected across an associated secondary winding, are effectively decoupled from each other while independently communicating with the line. In order to minimize the generation of line noise due to such an inherently unbalanced connection, it has already been proposed to insert two sections of the primary winding symmetrically in the two line wires between the transmitting network and a remote station.
In all these instances, the need for an inductive coupling prevents the use of integrated circuitry and consequently requires a relatively bulky and weighty structure.